MIT Open CourseWare - Free access to quite a few MIT courses that are on par with what you’d expect from MIT.

Open Culture - Compendium of free learning resources, including courses, textbooks, and videos/films.

Open YALE Courses - Open Yale Courses provides free and open access to a selection of introductory courses taught by distinguished teachers and scholars at Yale University.

Khan Academy – Watch thousands of micro-lectures on topics ranging from history and medicine to chemistry and computer science.

Zooniverse - Take part in a huge variety of interesting studies of nature, science, and culture.

TUFTS Open CourseWare - Tufts’ course offerings demonstrate the University’s strength in the life sciences in addition to its multidisciplinary approach, international perspective and underlying ethic of service to its local, national and international communities.

How Stuff Works? - More scientific lessons and explanations than you could sort through in an entire year.